The aim of the study was to investigate the effect of ethnicity, gender and age on the degree of clenching force and distribution of the load over the dentition. The maximal clenching force was measured in 12 young Danish females, 12 young Japanese females, 12 young Japanese males and 10 senior Japanese males using the Dental Prescale System. The occlusal contact area, average pressure, occlusal load, antero-posterior and right-left location of the occlusal load center (i.e., a center of balance of the occlusal load distributed over the maxillary dentition: OLC) and dental arch length and width were analyzed and compared. The arch width and average pressure in young Danish females were significantly smaller/lower than in Japanese females. The arch length, arch width, contact area and total occlusal load in young Japanese males were significantly greater than those of the Japanese females. The average pressure in young Japanese males was also greater than in senior males. The location of the OLC was almost the same in all groups. The results suggest that the analysis of the OLC may be a useful method for evaluating occlusal function and prosthodontic treatment because the location of the OLC is not affected by ethnicity, gender and age.

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: Electromyographic (EMG) activity was measured in the masseter muscle (Mm) , anterior temporalis (Ta) and posterior temporalis muscle (Tp) during maximal voluntary clenching (MVC) and recording occlusal contacts by black silicon method (RBS) on 12 normal subjects with sound dentitions.Intercuspal position (IP) , lateral position which was horizontally apart 1 mm from IP (LP-1) and canine's edge to edge lateral position (LP-E) were fabricated using LED mandibular tracking device ; MVC was performed at IP and LP-E on all subjects ; and RBS was at IP, LP-1 and LP-E on 9 subjects.Total muscle activity during RBS was about 10% of that during MVC at both IP and LP, but individual variation of EMG pattern exists. Ta and Tp showed significantly greater activity on the working side than the balancing side, while Mm showed no clear difference between the sides during both MVC and RBS at LP.The working side Ta showed significantly less activity during RBS than MVC at LP and was greatly affected by the clenching level, but while the balancing side Tp remained unchanged, activity was hardly affected.